Erosion principles

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January 2009www.ew.govt.nz

Guidelines for Soil Disturbing Activities

erosionsediment control


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erosion & sediment control Guidelines for Soil Disturbing Activities

erosion & sediment controlGuidelines for Soil Disturbing Activities

Erosion & Sediment ControlGuidelines for Soil Disturbing ActivitiesJanuary 2009

Environment Waikato Technical ReportNo.2009/02

Acknowledging the use of Auckland Regional Council TechnicalPublication Number 90: Erosion and Sediment Control Guidelinesfor Land Disturbing Activities in the Auckland Region.


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1. Principles 91.1 Types of Erosion 9

1.1 Factors Influencing the Erosion Process 11

1.2 The Ten Commandments of Erosion and Sediment Control 121.3 Types of Land Disturbing Activities Undertaken 14

2. Erosion Control Practices 172.1 Runoff Diversion Channel/Bund 19

2.2 Contour Drain 21

2.3 Watertable Drains 23

2.4 Water Cut-offs 252.5 Watertable Culverts 272.6 Sediment Pits 292.7 Berm bunds 31

2.8 Benched Slope 33

2.9 Rock Check Dam 35

2.10 Topsoil 372.11 Revegetation Techniques 39

2.11.1 Seeding 392.11.2 Hydroseeding 412.11.3 Mulching 43

2.11.4 Turfing 45

2.12 Geosynthetic Erosion Control Systems (GECS) 47

2.13 Stabilised Construction Entrance 49

2.14 Pipe/Flume Drop Structure 51

2.15 Level Spreader 55

2.16 Surface Roughening 57

3. Sediment Control Practices 593.1 Sediment Retention Pond 61

3.2 Silt fence 75

3.3 Super Silt Fence 79

3.4 Hay Bale Barrier 83

3.5 Stormwater Inlet Protection 85

3.6 Decanting Earth Bund 87

3.7 Sump/Sediment Pit 89

Table of contents


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4. Works Within A Watercourse 914.1 Temporary Watercourse Crossings 93

4.2 Temporary Watercourse Diversion 95

4.3 Permanent Watercourse Crossings 99

4.3.1 Bridges 101

4.3.2 Culvert Crossings 103

4.4 Rock Outlet Protection 107

5. Quarries 109

6. Vegetation Removal 1117. Glossary 115


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These guidelines have two main objectives:

a) To provide users, ranging from those directlyassociated with various soil disturbingactivities to interest groups, with a series ofcomprehensive guidelines for erosion andsediment control by:

outlining the principles of erosion andsediment control and the sediment transferprocess;

providing a range of erosion and sedimentcontrol practices to be implemented onvarious soil disturbing activities.

b) To minimise adverse environmental effects ofsoil disturbing activities through appropriateuse and design of erosion and sediment controltechniques.

How These Guidelines Work

These guidelines are based on the AucklandRegional Councils Technical PublicationNumber 90, titled Erosion and Sediment Control

Guidelines for Land Disturbing Activities.

These guidelines focus on the principles andpractices of erosion and sediment control forvarious soil disturbing activities. They should beused during planning for earthworks projects.They should also be used during the development

of an Erosion and Sediment Control Plan fora project and during development of consentapplications for earthworks projects. The erosionand sediment control measures and criteriaoutlined in these guidelines are minimumstandards and in many cases higher standardsmay be required.

The introduction to these guidelines describes theneed for erosion and sediment controls in theWaikato Region. Section 1 describes the basicprinciples of erosion and sediment control. Thissection describes basic types of erosion, factors

that influence the erosion process, the TenCommandments of erosion and sediment control,and common types of land disturbing activitiesundertaken in the Waikato Region. Section 2describes practices designed to prevent erosionfrom occurring. Section 3 describes practices forremoving sediment from water once erosion andsediment transport have occurred. Specific erosionand sediment control practices are sometimesrequired for works in watercourses, for quarriesand during vegetation removal, and these aredescribed in Sections 4, 5 and 6 respectively.

Finally, a glossary and references complete theguidelines.

Environment Waikato staff are availablefor further advice and can be contacted onEnvironment Waikatos Freephone0800 800 401.


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Erosion and Sediment Control in theWaikato Region

Significant areas of land are stripped ofvegetation or laid bare each year in the WaikatoRegion for construction of subdivisions, roads,cleanfills and other developments. Withoutprotection measures, transformation of this landcan result in accelerated on-site erosion andgreatly increased sedimentation of waterways,lakes, estuaries and harbours.

Significant quantities of sediment are dischargedfrom bare earth surfaces where appropriateerosion and sediment control measures are notimplemented.

Various studies indicate there is a 10 to 100 timesincrease in sediment yield from construction sitescompared with that produced from pastoral land,while data from the United States suggests thatthere may be up to 1000 times the sediment yieldfrom disturbed sites during construction comparedwith permanent forest cover.

The adverse ecological effects caused by sedimentin waterways include: Modified or destroyed in-stream values. Modified estuarine and coastal habitats. Smothering and abrading of fauna and flora. Changes in food sources and interruption of

lifecycles.

There is often a total change to in-streamcommunities. Recovery times from the effectsof sediment deposition are more likely to bemeasured in years rather than months. In addition

to ecological changes, there may be damageto water pumps and other structures, the qualityof water supplies usually diminishes, localisedflooding can occur and there is a loss of aestheticappeal.

Current Legislation

The Resource Management Act 1991 (RMA)establishes Environment Waikatos statutoryresponsibilities for resource management. Thepurpose of the RMA is to promote the sustainablemanagement of natural and physical resources.Sustainable management is defined in Section 5of the Act as:

managing the use, development and protectionof natural and physical resources in a way or at

a rate, which enables people and communitiesto provide for their social, economic, and culturalwellbeing and for their health and safety while:a) sustaining the potential of natural and physical

resources (excluding minerals) to meet thereasonably foreseeable needs of futuregenerations; and

b) safeguarding the life supporting capacity of air,water, soil and ecosystems; and

c) avoiding, remedying or mitigating any adverseeffects of activities on the environment.

Consents and Permitted Activities forEarthworks

Some earthworks activities require consents fromEnvironment Waikato. Consents may be requiredwhere earthworks are near streams, lakes,wetlands, or coastal waters, or where the worksare on steep land, or over large areas, or whenpermitted activity discharge standards cannot bemet. Consents may be required for stormwaterdischarges from earthworks sites. Large-scalevegetation clearance (such as forest harvesting)

and quarry operations may also require consents.Consent requirements are described in theWaikato Regional Plan. A copy of this Plan canbe found on our website www.ew.govt.nz.

Activities that do not require consents are calledPermitted Activities. The Waikato RegionalPlan also has conditions for Permitted Activitieswhich may apply to earthworks projects. It isvery important that where earthworks are beingundertaken as Permitted Activities, the conditionsof the Permitted Activity Rules are complied with

at all times. The permitted activity rules havestringent discharge standards which cannot beeasily met on larger sites. If the permitted activityrules discharge standards cannot be met at alltimes then resource consent/s should be obtained


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for the project. These Rules can be found onour website. If there is any doubt about theserequirements, you should contact EnvironmentWaikato.

When is Erosion and Sediment ControlRequired?

All projects involving soil disturbing activities inthe Waikato Region must incorporate erosionand sediment controls as an integral part ofdevelopment. On all projects, erosion and

sediment controls should be in place beforeearthworks commence and should be removedonly after the site has been fully stabilised toprotect it from erosion. The principles andpractices within these guidelines should bereferred to, and staff at Environment Waikatocontacted for further advice if required.

Works Within a WatercourseAny works within a watercourse must be carefullyplanned because controlling sediment generationfrom these activities is difficult. These guidelinesinclude a number of erosion and sediment controlmeasures that can used for realignment, piping,culverting and stabilisation works. Techniques forminimising sediment generation and dischargewhen undertaking works within a watercourse areoutlined in Section 4 of these guidelines. As statedin the introduction, consents may be requiredwhen undertaking such works, and contact shouldbe made with Environment Waikato staff todiscuss the specific details of the proposed activity.

CleanfillsThese guidelines do not include a specific sectionon cleanfill operations, but standard earthworkserosion and sediment control practices areappropriate for cleanfill operations.

Soils of the Waikato Region

Soils vary considerably throughout the Region.

Soils in the south-east of the Region (Taupo andthe upper catchments of the Waikato River) areformed from recent airfall tephra and can becategorised as weakly weathered and of lowcohesion. These are highly erodible pumice andraw volcanic soils which require a particular focuson control of overland flow when being worked.

The Waikato Basin and the Hauraki Plains arepredominantly loamlands derived from wellweathered tephra, some of which are river sorted.Although these soils are less erodible than therecent soils the presence of a clay component cancause visual effects and water quality degradationas a result of sediment laden runoff. This alsoapplies to localised highly weathered soils whichcan release high volumes of dispersive clayresulting in significant downstream effects.

Organic soils (peats) are also a major soil groupin the Waikato Basin and Lower Hauraki Plains.Working these soils does not normally resultin significant downstream effects apart from apossible increase in staining and debris.

The north of the Region (Pukekohe - Pukekawa)has much older Hamilton Ash soils which formwell structured, free draining, volcanic loamyclays. These soils generally have low erodibility,however because of the large ped size will entrainreadily in concentrated overland flow.

Clay soils, common in the Coromandel area,contain fine soil particles that take a much longertime to settle out of water than coarser silt sizedparticles. Larger and more numerous sedimentcontrol measures may not be very effective in

limiting the off-site transfer of sediment on claysoils. As a result more emphasis may be requiredon erosion control for clay soils compared to othersoil types.

The hill country of the Region has soils derivedfrom a variety of sedimentary parent materialranging from limestone around Waitomo tothe shattered mudstones of the Mokauiti Valley.Folded/ uplifted landforms in some cases hasresulted in soils on tilted parent material havingdeep seated mass movement. Erosion of this formmay require engineering solutions, which might

include such measures as drainage to reduce slipplane lubrication and buttress support.


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Types of Erosion1.1

Erosion is the process whereby the land surfaceis worn away by the action of water, wind, iceor other geological processes. The resultantdisplaced material is known as sediment.Sedimentation is the deposition of this erodedmaterial. Accelerated erosion, caused primarily byhuman development activities, is generally muchmore rapid than natural erosion.

The basic erosion process is detachment, transportand deposition (sedimentation). Water is the usualeroding agent and transport medium, throughraindrop impact and overland flow energy. Waterdislodges exposed soil particles and transportsthem downslope. Runoff and streamflow transportthe eroded soil particles to the final receivingenvironment where sedimentation occurs.

There are seven main types of erosion associatedwith soil disturbing activities:

1. Splash erosion2. Sheet erosion

3. Rill erosion4. Gully erosion5. Tunnel erosion6. Channel erosion7. Mass movement

Splash ErosionSoil erosion is a mechanical process that requiresenergy. Much of this energy is supplied by fallingraindrops.

The impact of a single raindrop on a soil surfaceor on a thin film of water may break up the soilaggregates and cause individual particles to bethrown into the air. If this occurs on a slope thensome particles will move upslope, but the neteffect due to gravity will cause splashed particlesto move downslope. Splash erosion is directlyrelated to the size, distribution, shape, velocity anddirection of the raindrop.

The erosive ability of splash erosion is enhancedby intense rainstorms.

Sheet ErosionWhen rainfall intensity exceeds the infiltrationrate of a soil and the capacity of the availablesurface detention, excess water moves downslope,

Sheet erosion or wash erosion is the uniformremoval of soil in thin layers by the forces ofraindrops and overland flow. It can be a verysignificant erosive process because it can coverlarge areas of sloping land and may go unnoticedfor some time. Sheet erosion can be recognisedby soil deposition at the bottom of a slope, or bythe appearance of light coloured subsoil materialon the surface. If left unattended, sheet erosion oftopsoils will gradually remove the nutrients andorganic matter important to re-vegetation, andwill eventually result in loss of soil productivityon contributing slopes and elevated sedimentconcentrations in receiving waters.

Rill ErosionRill erosion is the removal of soil by runoff movingin concentrated flows. As the flow changes fromsheet flow to deeper flow in these channels, or rills,the velocity and turbulence of the flow increases,and the energy of this flow is able to both detachand transport soil particles.

Rill erosion has been estimated to be the dominant

contributor to erosion on hill slopes.

Gully ErosionGully erosion is the removal of soil by runningwater resulting in the formation of channelsgreater than 300 mm deep. Gullies can bedistinguished from rills when normal agriculturaltillage operations cannot obliterate them.

The following are the processes which act informing gullies:

waterfall erosion at the head of the gully channel erosion raindrop splash diffuse flow from the side of the gully or from

seepage slides or mass movement of soil within the gully.

A gully may develop and grow rapidly and theirformation may generate a considerable amountof erosion. Therefore, their prevention andremediation is vital for erosion control.

Tunnel Erosion

Tunnel erosion, or piping is the removal ofsubsurface soil by subsurface water while thesurface soil remains relatively intact. This produceslong cavities beneath the ground surface, which

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supported, at which point the surface maycollapse forming a circular hole, sometimesreferred to as a tomo. Such erosion tunnels mayrange in size from a few centimetres to severalmetres in diameter and typically form a seriesalong the surface above a tunnel. Tunnel erosionis uncommon within Environment WaikatosRegion.

Channel ErosionThe erosion of ephemeral or perennial channelsresults from direct action of concentrated flowwhen the velocity or volume of flow in a streamincreases. Natural channels adjust over time tothe volume and velocity of runoff that normallyoccurs in the catchment. Channel erosion occursby scouring or undercutting of the stream bankbelow the water surface and generally happensduring medium to high flows.

High flows in stream channels occur morefrequently once a catchment has been developed,eroding stream banks and enlarging the channel.

Mass MovementMass movement is the erosion of soil or rock bygravity-induced collapse. It is usually triggeredby ground water pressure after heavy rain, butcan also have other causes, notably streamsundercutting the base of a slope or earthworks.Movement can be either rapid and nearinstantaneous (landslides, avalanches, debrisflows), or slow and intermittent (earth flows andslumps). Earth and soil slip movement are alsooften noted after the removal of vegetation fromcritical slopes associated with soil disturbingactivities. These slopes need to be identifiedbefore development starts and should be avoidedwherever practicable.

Mass movement can cause major problems, andgeotechnical investigations should be undertakenwhere possible to avoid critical slopes or allow forthe prevention of such erosion.

Fi 1 T f i i h W ik i


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Factors Influencing the Erosion1.1Process

The main factors influencing soil erosion areclimate, soil characteristics, topography, groundcover and evapotranspiration.

ClimateClimate affects erosion potential both directly andindirectly. The direct relationship arises from theaction of rain - a driving force of erosion - where

raindrops dislodge soil particles and runoff carriesthem away.

The annual pattern of rainfall and temperaturechange, by and large, determines the extent andgrowth rate of vegetation. This is critical, becausevegetation is one of the most important forms oferosion control.

Soil CharacteristicsFour soil characteristics are important indetermining soil erodibility:

Soil texture refers to the particle sizesmaking up a particular soil and their relativeproportions. Sand, silt and clay are the threemajor soil particle classes.

Organic matter improves soil structure andincreases permeability, water holding capacityand soil fertility.

Soil permeability refers to the ability of the soilto allow air and water to move through the

soil. Soils with a higher permeability produceless runoff at a lower rate than soils with lowpermeability. Engineered fills have a very lowpermeability, resulting in increased levels ofpotentially erosive runoff.

Soil structure is the degree that soil particlesare arranged into aggregates (peds). Agranular structure is the most desirable in bothagricultural and erosion control terms. Whenthe soil surface is compacted or crusted, watertends to runoff rather than infiltrate. Erosion

potential increases with increased runoff.

TopographySlope length and slope angle are critical factorsin erosion potential because they play a largepart in determining the velocity of runoff. Longcontinuous slopes allow runoff to build up velocityand to concentrate flow. This produces rill andgully erosion.

The shape of a slope also has a major bearingon erosion potential. The base of a slope ismore susceptible to erosion than the top becauserunoff arriving there is moving faster and is moreconcentrated. However, deposition may occur atthe base of concave slopes where slope anglediminishes.

Ground CoverGround cover includes vegetation and surfacetreatment such as mulches and geotextiles.Vegetation is one of the most effective long termforms of erosion control for protecting surfacesthat have been disturbed. Vegetation shields thesoil surface from the impact of falling rain, slowsthe velocity of runoff, holds soil particles in place

and maintains the soils capacity to absorb water.

EvapotranspirationDue to high evapotranspiration and reducedrainfall in the summer period, soil moisture levelsare often so low that irrigation or watering isneeded to achieve the moisture levels needed forplant growth. Evapotranspiration rates and thenumber of days of soil moisture deficit vary acrossthe Region. Careful consideration needs to begiven to evapotranspiration when attempting to

establish a vegetative cover and prevent erosion.


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The Ten Commandments of1.2Erosion and Sediment Control

1. Minimise DisturbanceFit land development to land sensitivity.

Some parts of a site should never be worked andothers need very careful working. Watch out forand avoid areas that are wet (streams, wetlands,springs), have steep or fragile soils or areconservation sites or features.

Adopt a minimum earthworks strategy (low impactdesign) - ideally only clear areas required forstructures or access.

Show all Limits of Disturbance on the Erosion andSediment Control Plan (E&SCP). On site, clearlyshow Limits of Disturbance using fences, signsand flags.

2. Stage ConstructionCarrying out bulk earthworks over the wholesite maximises the time and area of soil that isexposed and prone to erosion. Constructionstaging, where the site has earthworksundertaken in small units over time withprogressive revegetation, limits erosion.

Careful planning is needed. Temporary stockpiles,access and utility service installation all need tobe planned. Construction staging differs fromsequencing. Sequencing sets out the order ofconstruction to contractors.

Detail both construction staging and sequencingin the E&SCP.

3. Protect Steep SlopesExisting steep slopes should be avoided. Ifclearing is absolutely necessary. runoff fromabove the site can be diverted away from theexposed slope to minimise erosion. If steep slopesare worked and need stabilisation, traditionalvegetative covers like topsoiling and seedingmay not be enough - special protection is often

needed.

Highlight steep areas on the E&SCP showingLimits of Disturbance and any works and areas forspecial protection.

4. Protect WatercoursesExisting streams, watercourses, and proposeddrainage patterns need to be mapped. Clearingmay not be permitted adjacent to a watercourseunless the works have been approved.

Where undertaken, works that cross or disturbthe watercourse are also likely to require resourceconsents.

Map all watercourses and show all Limits ofDisturbance and protection measures. Show allpractices to be used to protect new drainagechannels. Indicate crossings or disturbances andassociated construction methods in the E&SCP.

5. Stabilise Exposed Areas RapidlyThe ultimate objective is to fully stabilise disturbedsoils with vegetation after each stage and atspecific milestones within stages. Methods are sitespecific and can range from conventional sowingthrough to straw mulching. Mulching is the mosteffective instant protection.

Clearly define time limits for grass and mulchcovers, outline grass species and define conditionsfor temporary cover in the case of severe erosionor poor germination in the E&SCP.

6. Install Perimeter ControlsPerimeter controls above the site keep cleanrunoff out of the worked area - a critical factor foreffective erosion control. Perimeter controls canalso retain or direct sediment laden runoff withinthe site. Common perimeter controls are diversion

drains, silt fences and earth bunds.

Detail the type and extent of perimeter controls inthe E&SCP along with design parameters.


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7. Employ Detention DevicesEven with the best erosion and sediment practices,earthworks will discharge sediment-ladenrunoff during storms. Along with erosion controlmeasures, sediment retention structures areneeded to capture runoff so sediment generatedcan settle out. The presence of fine grained soilsmeans sediment retention ponds are often nothighly effective. Ensure the other control measuresused are appropriate for the project andadequately protect the receiving environment.

Include sediment retention structure designspecifications, detailed inspection andmaintenance schedules of structures in the E&SCP.

8. Experience and TrainingA trained and experienced contractor is animportant element of an E&SCP. These peopleare responsible for installing and maintainingerosion and sediment control practices. Such staffcan save project time and money by identifyingthreatened areas early on and putting into placecorrect practices.

At each earthworks site, there should be a personwhose responsibility it is to oversee the erosionand sediment control practices. It is often usefulfor Environment Waikato monitoring staff to meetwith this person for a pre-construction meeting,for regular inspection visits (including a pre-wintering meeting), and a final inspection. Fordetails about available erosion and sedimentcontrol courses, contact Environment Waikato.

9. Make Sure the Plan EvolvesAn effective E&SCP is modified as the projectprogresses from bulk earthworks to projectcompletion. Factors such as weather, changesto grade and altered drainage can all meanchanges to planned erosion and sediment controlpractices.

Update the E&SCP to suit site adjustments intime for the pre-construction meeting and initialinspection of installed erosion and sedimentcontrols, and make sure it is regularly referred toand available on site.

10. Assess and AdjustInspect, monitor and maintain control measures.

Assessment of controls is especially importantfollowing a storm. A large or intense storm willleave erosion and sediment controls in need ofrepair, reinforcement or cleaning out. Repairingwithout delay reduces further soil loss andenvironmental damage.

Assessment and adjustment is an importanterosion and sediment control practice - make sureit figures prominently in the E&SCP.

Assign responsibility for implementing the E&SCPand monitoring control measures as the projectprogresses.


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Types of Land Disturbing1.3Activities Undertaken

The following are the main types of soil disturbingactivities undertaken in the Waikato Region, whichmay require the use of erosion and sedimentcontrols, and these are discussed in theseguidelines:

1. trenching2. watercourse works3. cleanfills

4. small sites (such as house lots)5. earthworks/projects (major cut to fill)6. roading/tracking7. quarries and vegetation removal.

The following is a brief summary of keyconsiderations for minimising adverseenvironmental effects of these activities that arenot found in the detailed description of erosionand sediment control measures in sections 2 and3 of the guidelines.

TrenchingTrenching, usually for installing utility services,often happens towards the end of the bulkearthworks phase of a project. The followingpoints need to be considered when trenching.

The project needs to be undertaken inappropriately sized stages such that the areaexposed can be fully stabilised within anacceptable timeframe.

If trenching affects existing erosion and

sediment control measures that are part of theoverall development, those measures shouldbe reinstated as soon as possible. Contingencymeasures should be put in place until theoriginal measures are reinstated or replaced.

All trenching operators working within a largersite must be familiar with the overall Erosionand Sediment Control Plan for the site andmust comply with this approved plan.

Independent erosion and sediment controlmeasures detailed in these guidelines shouldbe employed for the trenching operation.

Topsoil and subsoils should be stockpiledseparately adjacent to the trench so that atthe completion of the operation, these soilscan be replaced in the appropriate order andvegetation established.

When trenching through overland flow paths,give special consideration to the diversion ofany flows, which may occur during trenching,as well as reinstating and stabilising theoverland flow path.

Works Within a WatercourseWorks within a watercourse should be avoidedwherever possible, with all alternatives consideredbeforehand. Where watercourse works areunavoidable, they will create sedimentationdownstream, so the following points should becarefully considered when undertaking theseworks.

Have all alternatives been considered?

Install a stabilised diversion so that works can

be undertaken in the dry and reinstate thestream flow only after these areas have beenappropriately stabilised. If a diversion is nota viable option, then ensure the alternativeoptions are fully considered.

Carry out works during a dry time of the yearwhen stream flows are low and the likelihoodof a storm is low.

Keep the duration of works short.

Identify in-stream values so as to avoid criticalperiods such as fish spawning periods and thewhitebait season.

Consider the direct short and long termimpacts of culverts or in-stream structuresand install appropriately designed fish-passprovisions.

Be sure to inform all downstream users, forexample water-users, of potential downstreamsediment discharges.


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CleanfillsCleanfills dispose of unwanted fill material.

Soil disturbing activities associated with cleanfillsrange from haul roads and access areas to tipfaces and dumping areas. Several controls areneeded for adequate erosion and sedimentcontrol on such sites and the following pointsshould be carefully considered when undertakingsuch operations:

Erosion and sediment controls should beinstalled in accordance with these guidelinesand appropriate maintenance undertaken.

Staging of cleanfill operations is critical and aprogramme of progressive stabilisation of allcleanfill sites should be part of each operation.

Small SitesThe cumulative impact from small sites can beconsiderable and in some areas may cumulativelydischarge as much sediment as large earthworkssites. Often, stormwater systems are in place but

there are no, or minimal, erosion and sedimentcontrols on the site. This results in sedimentdischarging through an efficient conveyancesystem (the stormwater system) directly to thereceiving environment.

The following points need to be considered whenundertaking small site development:

Erosion and sediment controls should beinstalled either on an individual site-by-site basis or a combination of the sites, in

accordance with these guidelines. Stormwater runoff from small sites needscareful planning in terms of the location ofroof down pipes so that runoff across bare sitesdoes not scour soils.

Areas of exposed soils should be stabilisedupon completion of earthworks, includingtopsoil and subsoil stockpiles, lawn areas andaccessways.

EarthworksEarthworks include a wide range of activities fromcleanfilling operations (defined above) through toearthworks associated with industrial, commercialand residential developments. Earthworks havea major potential to generate large amounts ofsediment, and if not controlled appropriately,can lead to large sediment discharges. Planningof these developments is critical to ensure thatthe activity is undertaken appropriately, andin a controlled manner to avoid unnecessaryimpacts on receiving environments. The TenCommandments outline the critical features of anearthworks operation.

The following are further key points contractorsneed to be aware of when undertaking earthworksoperations.

Emphasis should be placed on erosioncontrol, rather than sediment control, becausepreventing sediment generation is the bestmeans of preventing sediment discharge fromearthworks sites.

Always produce an Erosion and Sediment

Control Plan (E&SCP) for an earthworksoperation. Be sure that all parties involved withthe operation, including subcontractors, arefamiliar with and have access to a current copyof this Plan.

Always update the E&SCP with major variationson the site. Keep this up-to-date version in thesite office at all times.

Plan ahead and undertake consultation withnecessary parties as required.

Install appropriate controls in accordancewith the E&SCP and be sure that the design

specifications are appropriate for theoperation. Install subsurface drainage as required (to

an agreed methodology) to divert subsurfaceclean water past control structures and areas ofdisturbance as appropriate.


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Roading/TrackingLike trenching, the linear nature of roading poseschallenges for erosion and sediment control.Measures need to be carefully planned to ensurecontrols are successful. Often the operation canbe undertaken sequentially, stabilising workedareas as they are completed. This minimises thetotal sediment generating area of the proposaland helps prevent unnecessary road maintenance.

The following are some key points to considerwhen working through a roading proposal.

Provide enough room for effective erosion andsediment control measures. Often the roadcorridor itself can involve the whole designationarea and no room remains for such controls.Where space is a constraint, make sure thatthe erosion and sediment controls will give thenecessary protection to downstream receivingenvironments.

Incorporate stormwater design into the E&SCP.This removes the need to revisit the area toinstall stormwater systems and the unnecessaryextra earthworks that their construction would

require. Keep the areas of road corridor exposed at

any one time to a limit that can be practicallystabilised with hardfill or by vegetative means,to minimise the exposed area at risk.

When crossing watercourses, look foralternative routes and alternative designs andimplement the option which provides the bestenvironmental alternative.

Control all upslope catchment runoff, divertingclean water around or safely through the areaof disturbance.

Quarries and Vegetation RemovalMeasures in these guidelines are suitable forquarry and vegetation removal operations.However, the long term nature of many quarriesand the clear felling of whole catchments duringvegetation removal operations mean that somespecial erosion and sediment control measuresneed to be implemented. Careful planning ofsuch operations is thus critical. The key areaswhere attention is required are discussed in detailin sections 5 and 6 of these guidelines and should

be read in conjunction with the other erosion andsediment controls also detailed.


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Sections 2 and 3 outline minimum criteria for thedesign, construction and implementation of arange of erosion and sediment control measurescommonly used on earthworks sites and on othersoil disturbing activities. These measures form oneaspect of erosion and sediment control on anysite, and should always be used in conjunctionwith the measures outlined in the Ten Principlesof Erosion and Sediment Control in Section 1 ofthese guidelines.

The most effective form of erosion control is tominimise the area of disturbance, retaining asmuch existing vegetation as possible. This isespecially important on steep slopes or in thevicinity of watercourses, where no single measurewill adequately control the erosion and transportof sediment, and where receiving environmentsmay be highly sensitive.

The criteria outlined are the minimum standardfor each measure. Each soil disturbing activitymust be assessed on an individual basis, and inmany cases higher standards may be required.

For every practice, these guidelines outline thefollowing: definition purpose application design/construction specifications comments maintenance.

Symbols shown alongside controls are listed inAppendix 1.

Erosion Control Practices2.


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DefinitionA non-erodible channel or bund for theconveyance of runoff constructed to a site-specificcross section and grade design.

PurposeTo either protect work areas from clean upsloperunoff (clean water diversion), or to divertsediment-laden water to an appropriate sedimentretention structure.

ApplicationRunoff diversion channels/bunds are used in thefollowing situations:

To divert clean upslope water away from areasto be worked (clean water diversion).

To divert sediment-laden runoff from disturbedareas into sediment treatment facilities.

At or near the perimeter of the constructionarea to keep sediment from leaving the site.

In either temporary or permanent situations. Keep permanent diversions in place until the

disturbed area is permanently stabilised againsterosion.

Stabilise runoff diversion channels/bunds

Runoff Diversion Channel/Bund2.1

DesignThere are many designs for runoff diversionchannels/bunds. The following outlines minimumdesign criteria requirements. Design the runoff diversion channel/bund to

carry the flow from the critical 20 percent AEPrainfall event,1 in 5 year return period storm(plus 300 mm freeboard after settling).

Restrict use to grades no more than 2 percentunless armoured with geotextile or suitablysized rock.

Cleanwater diversion channels must bearmoured with geotextile and/or rock sufficientto prevent any erosion of the channel.

Cleanwater diversion bunds must be rapidlyvegetated unless they are armoured withgeotextile sufficiently to prevent erosion.

Achieve rapid vegetative stabilisation ofcleanwater diversion bunds by hydro-seedingand mulching the exposed bund surface.Alternative methods of stabilising cleanwaterdiversion bunds may be used if EnvironmentWaikato approval has been obtained.

Incorporate stabilisation measures (such as geotextile, vegetative stabilisation or rock

armouring) to prevent erosion. Construct with a trapezoidal cross sectional

shape with internal side slopes no steeper than

Plate 1: Runoff Diversion Channel


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Fi 3 R ff Di i Ch l

Construct runoff diversion bunds with sideslopes no steeper than 3:1.

Survey all gradients on the site. Ensure earth embankments used to construct

runoff diversion channels/bunds areadequately compacted.

Flow velocities greater than 1 m/s will causethe runoff diversion channel/bund to erode.

Incorporate a stable erosion-proof outfall (suchas a level spreader) to reduce water velocitiesand prevent scour at the outlet.

Ensure the runoff diversion channel/bundoutlet:- functions with a minimum of erosion- directs clean runoff onto an undisturbed/

stabilised area- directs flows containing sediment into a

sediment retention structure- is located in such a position that ideally suits

the field conditions.

Considerations Consider designing an emergency overflowsection or bypass area to limit damage fromstorms that exceed the design storm.

Avoid abrupt changes in grade which can leadto sediment deposition and overtopping, orerosion.

MaintenanceRunoff diversion channels/bunds need regularmaintenance to keep functioning throughouttheir life. Regular maintenance consists of thefollowing: Inspect after every rainfall and during periods

of prolonged rainfall for scour and areas wherethey may breach.

Repair immediately if required to ensure thatthe design capacity is maintained.

Remove any accumulated sediment depositedin the runoff diversion channel/bund due to lowgradients and velocities.

Carefully check outlets to ensure that theseremain free from scour and erosion.

Figure 2: Clean Water Diversion Channel


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DefinitionA temporary ridge or excavated channel, orcombination of ridge and channel, constructed toconvey water across sloping land on a minimalgradient.

PurposeTo break overland flow down disturbed slopes bylimiting slope length and thus the erosive powerof runoff, and to divert sediment laden water to

appropriate controls or stable outlets.

ApplicationUse contour drains in the following situations: At intervals across disturbed areas to shorten

overland flow distances. As temporary or daily controls. To split and direct flow from disturbed areas to

runoff diversion channels/bunds.

Design (refer to Figure 4)Ensure gradients are no greater than 2 percentand the contour drains are kept as short aspracticable in order to minimise erosion. The

Contour Drain2.2

Plate 2: Contour Drain


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positioning of contour drains is often determinedby the necessity for stable outfalls, but in generalthe following spacing applies:

Table 1: Positioning of Contour Drains

Slope of Site Spacing of ContourDrains

(%) (m)

5 50

10 40

15 30

Maintenance Install contour drains at the end of each day. Inspect contour drains after every rainfall and

during periods of prolonged rainfall.

Immediately carry out any maintenance that isrequired.

Figure 4: Contour Drain


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DefinitionA channel excavated parallel to a road or track.

PurposeTo provide permanent underfill drainage of thecarriageway and/or to provide a conveyancechannel for stormwater.

ApplicationThis practice applies primarily to permanentroading where it is necessary to provide a degreeof underfill drainage of the carriageway to ensureroad stability and/or where upslope storm flowsand storm flows arising from the carriageway itselfare required to be conveyed to an erosion proofoutfall.

Design (refer to Figure 5)The following outlines design criteriarequirements. Design the watertable drain to carry the flow

from the critical 10 percent AEP rainfall event. Watertable drains with greater than 2 percent

gradient may need to be armoured (referTable 2).

Armouring is normally done with appropriatelysized aggregate compacted into the invert ofthe drain and laid at an appropriate depth.Alternatives are site concrete and corrugatedfluming or a series of check dams.

Construct with a cross sectional shape with aslarge an invert width as practicable to minimiseflow velocities - refer Figure 3.

Position rock check dams along steep sectionsto provide additional armouring.

Table 2: Watertable Drain Amouring

Slope (%) Aggregate size D50 mm

0-5 Controlled using appropriately

spaced culvert outfalls

5-10 Standard basecourse

10-15 80mm

15-20 120mm

Considerations Consider armouring the area adjacent to thedrain by vegetative means. This can assist inthe long-term stability of the drain edges andvegetative growth within the watertable drainitself can assist in stabilising the drain invert.

If possible, avoid the use of watertabledrains on low-cohesive soils to minimise theconcentration of overland flow. If constructingfarm tracks in these soils provide a slight fallaway from the slope to shed runoff evenlyalong the length of the track.

Avoid abrupt changes in grade that can bedifficult to armour.

Make the invert of the watertable drain is aswide as practicable to minimise flow velocities.

Maintenance Check the watertable drain after the first major

storm event for weak points in the armouringand strengthen accordingly.

Excessive weed growth can be controlledusing appropriate herbicides. However, ifthe drain is sized correctly in the first place a

total grass cover should not interfere with theproper operation of the drain, and herbicideapplication should not be necessary.

Removal of accumulated sediment generatedfrom the upslope catchment is generallyundertaken using an excavator, shaping thedrain to the original profile and re-armouring.

Watertable Drains2.3


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Compacted Earth Fill

Cut

5% Crown or slopetowards the insidewater table drain

Culvert

Stabilised outfall ie:Flume

Culvert pit

Cut face stabilised byvegetation

Carriageway

Buried culvert

Stabilised outfall

Flow

Culvertpit

Plan View

Culvert Pit Cross Section XX

Flow

0.5m dead storage

Culvert

Berm

Carriageway Crown

Rock amouring

Rock Check Dam toincrease head aboveculvert therebyincreasing culvertflows

Figure 5: Watertable Drain


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DefinitionAn excavated channel combined with acompacted earth bund extending more or less atright angles across the carriageway and berm, toa stable outfall.

PurposeTo provide temporary or permanent drainageof surface water off the carriageway at regularintervals to prevent the concentration of overlandflow.

ApplicationThis practice applies primarily to low use roadingand tracking where storm flows arising fromupslope of the road and the carriageway itselfare required to be conveyed to an erosion proofoutfall.

Design (refer to Figure 6)The following outlines design criteriarequirements.

Construct the water cut-offs out of compactedcompetent material and make them sufficientlylarge to prevent overtopping. Modification ofthe standard design detailed may be requireddepending on the type of vehicles.

The channel invert may require armouring withaggregate to prevent scour.

The channel invert should have a gradient of2-5 percent to prevent build up of sediment.This may necessitate angling the cut-off up to30 degrees downslope to get sufficient fall onlow gradient sections of carriageway.

Construct with a cross sectional shape ofthe channel with as large an invert width aspracticable to minimise flow velocities.

Compact fill material into the inside berm areato prevent outflanking.

Considerations Consider vegetating the track and the cut-off tominimise erosion.

Avoid placing cut-offs on steep short sectionswhere braking of vehicles can cause stabilityproblems, particularly if cut-offs can be placedon lesser gradient immediately above thesection.

Endeavour to outfall the cut-offs onto stablewell vegetated in situ ground.

Maintenance Check the water cut-off after the first major

storm event for weak points and strengthenaccordingly.

Install additional cut-offs as required. Regular maintenance may be required if stock

tracking occurs.

Water Cut-offs2.4


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Table 3: Typical Water Cut-off Spacing check

Slope (%)

Soil Type:

Spacing (m)

Cohesive

Low Cohesion

0-5 50 60

5-10 40 50

10-15 30 40

15-20 20 30

20-30 10 20

>30


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DefinitionA surface flow conveyance structure connectingthe watertable drain to a stable outfall.

PurposeTo provide a permanent flow conveyance structureunder a carriageway.

ApplicationThis practice applies primarily to permanentroading where it is necessary to prevent theconcentration of overland flow in the watertabledrain by providing regular drainage points to anerosion proof outfall.

Design (refer to Figure 7)The following outlines design criteriarequirements:

Design the watertable culvert to carry the flowfrom the critical 10 percent AEP rainfall event.The efficiency of the culvert will depend on the

inlet geometry so every effort should be madeto ensure a smooth entry into the culvert inlet.

Watertable culverts should be placed with agradient of 5-8 percent to ensure self cleaning.

Generally watertable culverts (pipes) should notbe smaller than 300 mm diameter to minimiseentrance blockage.

A culvert pit up to 1m deep is generallyconstructed at the entrance to the watertableculvert. The culvert inlet should be about 0.5 mabove the invert of this pit.

The spacing of watertable culverts will depend

on the surface area of the carriageway, theupslope catchment and the erodibility of thein situ soils. Spacing will also depend on thelocation of stable outfalls ie well vegetatedspurs or ridges where flows can be dissipated.

Consider constructing rock check dams in thewatertable drain immediately below the culvertinlet to improve culvert inlet efficiency.

Considerations Define stable outfall points and install culverts

to these points first. If possible, avoid discharges to fill areas as

these will require armouring or drop structures. Surface fluming (tanalised 150 x 50) can be

used on farm tracks however debris build-up isgenerally high, requiring regular maintenance.

Grading a farm track to have a series of humpand hollows can provide a low cost alternative

to regularly spaced culverts. The increased gradient into the culvert pit.

Maintenance Check the watertable culvert after the first

major storm event for blockage and thestability of the outfall.

Check the culvert pit for sediment/debris andremove.

Table 4: Typical Watertable CulvertSpacing

Slope (%) Spacing (m)

Soil Type: Low Cohesion Cohesive

0-5 50 60

5-10 40 50

10-15 30 40

15-20 20 30

20-30 10 20

>30


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Cut face(hydroseedingrecommended)

Overlandflow

Fill facestabilised bytopsoiling,grassing andmulchingWatertable

drain

Flume

Culvert buried witha 5-8 deg fall

Carriageway

StabilisedOutfall

Rock CheckDam

Watertable Drain invert

Table 4: Typical Watertable Culvert Spacing

Slope (%)

Soil Type:

Spacing (m)

Low Cohesion

Cohesive

0-5 50 60

5-10 40 50

10-15 30 40

15-20 20 30

20-30 10 20

>30


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DefinitionAn excavation that acts as a soakage bay,whereby stormwater runoff is collected and left tosoak into the ground.

PurposeTo provide temporary or permanent drainagecontrol of stormwater runoff from roads andtracks, constructed on non-cohesive soils, byretaining water for ground soakage and trappingsediment on site.

ApplicationSediment pits can be used in the followingsituations:

To drain watertables on the edges of roads ortracks.

On free-draining soils such as alluvium pumiceor ash.

On natural ground as long as slopes are nottoo steep.

In conjunction with water cut-offs.

DesignThe following outlines design criteriarequirements:

Excavate sediment pits to at least one metredepth.

Always install sediment pits in undisturbed(natural) soil.

The slope of the inlet should be reasonably flat(1H:5V) to avoid erosion problems.

Generally, sediment pits are located to suitthe terrain. As a guideline: for slopes 12 percent, have sediment pits every 30 m to10 m.

Considerations Do not place sediment pits on blind areas of

the road where they might be a safety hazardfor vehicles.

Ensure overtopping flows discharge over level,well-vegetated in situ ground.

MaintenanceSediment pits require regular cleaning to maintainstorage volume and to prevent the floor of thesediment pit from sealing with the settlement offine sediments over time.

Figure 8: Sediment pits

Sediment Pits2.6


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DefinitionAn aggregate bund constructed on the outsideberm parallel to the carriageway.

PurposeTo provide permanent diversion of stormwateraway from erosion prone fill batters.

ApplicationThis practice applies primarily to permanentroading where it is necessary to directcarriageway runoff to an erosion proof outfall. Itnormally applies to the conveyance of flows alongthe berm of an inside bend, however can also beused effectively on both sides of a culvert crossingwhere carriageway flows tend to concentrate.

DesignThe following outlines design criteriarequirements. Design the berm bund to carry the flow from

the critical 10 percent AEP rainfall event.

Outfall flows to a level area of berm if possiblewhere flows can dissipate over a wide area.

ConsiderationsIf possible, avoid the use of berm bunds on low-cohesive soils to minimise the concentration ofoverland flow. If constructing farm tracks in thesesoils provide a slight fall away from the slope toshed runoff evenly along the length of the track.

Avoid abrupt changes in grade that can be

difficult to armour.

MaintenanceCheck the berm bund after the first major stormevent and periodically for weak points in thearmouring and strengthen accordingly.

Berm bunds2.7


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DefinitionModification of a slope by benching to divertrunoff to an appropriate conveyance system.

PurposeTo limit the velocity and volume, and hence theerosive power, of water moving down a slope andtherefore minimising erosion of the slope face.

ApplicationBenched slopes are primarily used on long slopesand/or steep slopes where rilling may be expectedas runoff travels down the slope. . The spacingof the benched slopes and the specific conditionsfor which they apply depend on slope height andangle, and the nature of the soil/material beingbenched. The primary purpose is to prevent theconcentration of runoff which, in turn, increaseserosion.

Benched Slope2.8

Plate 3: Benched Slope

Table 5: Benched Slope Design

Slope Angle Vertical Height Between

Benches

(%) (m)

50 10

33 15

25 20


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Design Provide benched slopes for slopes exceeding25 percent - see Table 5.

Locate benched slopes to divide the slope faceas equally as possible and convey the water fromeach bench to a stable outlet. Soil types, seepsand location of rock outcrops need to be takeninto consideration when designing benchedslopes.

Ensure benched slopes are a minimum of 2 mwide for ease of maintenance.

Design benched slopes with a reverse slope of15 percent or flatter to the toe of the upper slopeand with a minimum depth of 0.3 m. Keep thegradient of each benched slope to its outletbelow 2 percent, unless design, stabilisationand calculations demonstrate that erosion risk isminimised.

Keep the flow length along a benched slope toless than 250 m unless design and calculationscan demonstrate that erosion risk is minimised.

Divert surface water from the face of all cut and/or fill slopes of benched slopes by the use ofrunoff diversion channels/bunds except where:- the face of the slope is not subject to any

concentrated flows of surface water such asfrom natural drainage, channels or otherconcentrated discharge points, and

- the face of the slope is protected by specialerosion control materials including, but notlimited to, approved vegetative stabilisationpractices, rip-rap, or other approvedstabilisation methods.

Provide subsurface drainage where necessaryto intercept seepage that would otherwiseadversely affect slope stability or createexcessively wet site conditions. Check therequirements of the city or district council.

Do not construct benched slopes close toproperty lines where they could endangeradjoining properties without adequatelyprotecting such properties againstsedimentation, erosion, slippage, settlement,subsidence or other related damages. Checkthe requirements of the city or district council.

Stabilise all disturbed areas.

Construction Specifications Compact all fills to reduce erosion, slippage,

settlement, subsidence, or other relatedproblems.

Keep all benched slopes free of unconsolidatedsediment during all phases of development.

Permanently stabilise all graded areasimmediately on completion of grading.


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Plate 4: Rock Check Dam

DefinitionSmall temporary dam constructed across achannel usually in series, to reduce flow velocity.May also help retain sediment.

PurposeTo reduce the velocity of concentrated flows,thereby reducing erosion of the channel. Whiletrapping some sediment, they are not designed tobe used as a sediment retention measure.

ApplicationThis practice applies primarily to earthworks siteswhere it is necessary to slow velocity of flowsin order to prevent erosion. Do not use rockcheck dams in a perennial watercourse. Specificapplications include the following. Temporary channels which, because of their

short length of service, are not suitable for non-erodible lining but still need some protection toreduce erosion.

Permanent channels which for some reason

cannot receive a permanent non-erodiblelining for an extended period of time.

Temporary or permanent channels whichneed protection during the establishment of a

t ti

Rock Check Dam2.9

Design Ensure the catchment in question has a

contributory drainage area of less than 1 ha. Direct all flows over the centre of the rock

check dam. Construct each rock check dam with a

maximum centre height of 600 mm. Build thesides 200 mm higher than the centre to directflows to the centre. Do not use rock checkdams as a primary sediment trapping facility.Ensure that any sediment laden runoff passes

through a sediment trapping device or devicesbefore being discharged from the site.

Supply specific design and calculations if rockcheck dams are to be used on catchmentsgreater than 1 ha.

Place a mix of 100 mm to 300 mm diameterwashed rock to completely cover the width ofthe channel. In steeper catchments use largersized rock (0.5 - 1.0 m) on the downstreamside of the rock check dam.

Ensure rock batter slopes are 2:1. Locate rock check dams at a spacing so that

the toe of the upstream dam is equal in heightelevation to the crest of the downstream one.

Ensure the toe of the upstream dam is neverhigher than the crest of the downstream dam.


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Table 6: Rock Check Dam Design

Slope Spacing Between Dams (m)

450 mm

Centre Height

600 mm

Centre Height

2% or less 24 30

2% to 4% 12 15

4% to 7% 8 11

7% to 10% 5 6

Over 10% Utilise stabilised

channel

Utilise Stabilised

Channel

MaintenanceWhile this measure is not intended to be usedprimarily for sediment trapping, some sedimentcan accumulate behind the rock check dams.Remove this sediment when it has accumulated to50 percent of the original height of the dam.

When temporary channels are no longer needed,remove rock check dams and fill in the channel.

In permanent channels, remove rock check damswhen a permanent lining can be installed. In the

case of grass lined ditches, rock check dams maybe removed when grass has matured sufficientlyto protect the channel. The area beneath the rockcheck dams needs to be seeded and mulched orstabilised with appropriate geotextile immediatelyafter removing the dams.

Figure 10: Rock Check Dam

1.635300mm min

450mm min600mm max

SPACING (SEE TABLE BELOW)

SLOPE/FLOW

Elevation

Cross Section xxStandard Rock Check Dam

Downstream face at a slope of 2:1

Rock size to be 100mm to 300mm mix

200mm min


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DefinitionThe placement of topsoil over a prepared subsoilprior to the establishment of vegetation.

PurposeTo provide a suitable soil medium for vegetativegrowth for erosion control while providing somelimited short term erosion control capability byprotecting subsoils and absorbing water.

ApplicationTop soiling is recommended in the followingsituations:

Where the texture and/or the organiccomponent of the exposed subsoil or parentmaterial can not produce adequate vegetativegrowth.

Where the soil material is so shallow that therooting zone is not deep enough to supportplants or furnish continuing supplies ofmoisture and plant nutrients.

Where high quality turf and landscape

plantings are to be established.

Generally top soiling is combined with vegetationestablishment and is not seen as an erosioncontrol measure in itself. Top soiling as a shortterm stand alone erosion control measure islimited to sites with an average slope of less than5 percent with contour drains installed as perthese guidelines and for periods of less than twoweeks only.

Top soiling alone will not provide sufficient erosion

protection to allow sediment control measures tobe removed.

When staging within an earthworks operation, topsoiling as a treatment in itself is not acceptableand other means of stabilisation such as re-vegetation will also be required.

DesignNot applicable.

Construction SpecificationsOnce site shaping work has been completed,evenly spread a minimum of 100 mm of topsoilbefore re-vegetating. On steeper sites (over25 percent), scarify the subsoils to a depth of aleast 100 mm to ensure bonding between topsoiland subsoil before applying topsoil.

Incorporate surface roughening into all top soilingoperations in accordance with these guidelines.

In general topsoil has a beneficial effect in lightrain because it can hold more moisture than theunderlying clay material. However, during heavyrain, topsoil will become saturated and rill erosionand slumping can result. For this reason it isimportant to establish a full vegetative cover assoon as possible and retain all sediment retentionfacilities on the site until a vegetative cover is fullyestablished.

MaintenanceCheck the condition of the topsoil on a regularbasis and re-grade and/or replace wherenecessary so as to always maintain the 100mm minimum depth of topsoil and surfaceroughening.

Topsoil2.10


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DefinitionThe planting and establishment of quick growingand/or perennial vegetation to provide temporaryand/or permanent stabilisation on exposed areas.

PurposeSeeding is designed to stabilise soil on disturbedareas to reduce sediment and runoff todownstream or off-site areas.

Application Seeding

This practice applies to any site whereestablishing vegetation is important to protectbare earth.


Construction Specifications Site Preparation

Before seeding, install all required erosion and

sediment control practices such as diversionchannels and sediment retention structures.Grade the site as necessary to permit the useof conventional equipment for soil preparation,seeding and maintenance.

Seed Bed PreparationPrepare a good seed bed to ensure successfulestablishment of vegetation. Take care toensure that the seed bed is free of large clods,rocks and other unsuitable material. Applytopsoil at a minimum depth of 100 mm to

allow for a loose and friable soil surface.

Soil AmendmentsApply fertiliser as outlined in Table 7 of theseguidelines. This fertiliser application rate canbe varied with the approval of EnvironmentWaikato. For large sites or unusual siteconditions it is advisable to have soil fertilitytests done. Some soils may require the additionof lime toimprove pH.

SeedingApply seed at a mixture and rate as in Table7 of these guidelines. This seeding rate canbe varied with approval from EnvironmentWaikato. Apply the seed uniformly and sow atthe recommended rate. Seed that is broadcastmust be covered by raking and then lightlycompacted into place. If hydroseeding isrequired, then it can be utilised in accordancewith Section 2 of these guidelines.

MulchingWhen working on steep sites (greater than20 percent) or during the winter period(between May 1 and September 30) mulchingwill need to be applied in accordance withSection 2 of these guidelines immediatelyfollowing seeding.

IrrigationAdequate moisture is essential for seedgermination and plant growth. Irrigation canbe very helpful in establishing vegetationduring dry or hot weather conditions or onadverse site conditions. Irrigation must be

carefully controlled to prevent runoff andsubsequent erosion. Inadequate or excessiveirrigation can do more harm than good.

MaintenanceRe-seed where seed germination is unsatisfactoryor where erosion occurs. In the event ofunsatisfactory germination after May 1, the areawill also require the application of mulch inaccordance with Section 2 of these guidelines.

Depending on site conditions it may be necessaryto irrigate, fertilise, oversow or re-establishplantings in order to provide vegetation foradequate erosion control. See Table 7 of theseguidelines for details of maintenance fertiliserapplications.

Protect all re-vegetated areas from traffic flowsand other activities such as the installation ofdrainage lines and utility services.

Revegetation Techniques2.11

Seeding2.11.1


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Table 7: Grass Seed and Fertiliser Application Rates

Mix Rate (kg/ha)

Seeding types Perennial Ryegrass

Brown Top with a

Red/White Clover mix

Perennial - 90

Brown Top - 30

Clover - 30

FertiliserApplication

D.A.P. (Di-Ammonium Phosphate)

or similar

240


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DefinitionThe application of seed, fertiliser and paper orwood pulp with water in the form of a slurry,sprayed over the area to be re-vegetated.

PurposeTo establish vegetation quickly while providing adegree of instant protection from raindrop impact.

ApplicationThis practice applies to any site where vegetationestablishment is important for the protection ofbare earth surfaces. For example:

Critical areas on the site prone to erosion suchas steep slopes and sediment retention pondbatters.

Critical areas on the site that cannot bestabilised by conventional sowing methods.

Around watercourses or runoff diversionchannels where rapid establishment of aprotective vegetative cover is required beforeintroducing flows.


Construction SpecificationsThe seed generally adheres to the pulp whichimproves the microclimate for germination andestablishment. This method allows vegetationto establish on difficult sites and can extend intocooler winter months provided it is utilised withmulching.

Site PreparationBefore hydroseeding, install any needederosion and sediment control practices suchas runoff diversion channels. Scarify any steepor smooth clay surfaces to improve retentionof the hydroseeding slurry. Hydroseedingspecifications need to be verified byEnvironment Waikato prior to implementation,with recommended seeding and fertiliserapplication rates outlined in Table 7 of theseguidelines.

WateringHydroseeding requires moisture forgermination and growth. Becausehydroseeding is often used for difficult sites,the timing of the application to get favourable

growing conditions is an important factor.

MaintenanceHeavy rainfall can wash hydroseedingaway, particularly from smooth clay surfacesand overland flowpaths. Where vegetationestablishment is unsatisfactory the area mayrequire hydroseeding again. In the event ofunsatisfactory germination after May 1, thearea will also require mulching in accordancewith Section 2 of these guidelines.

Protect all re-vegetated areas from traffic flowsand other activities such as the installation ofdrainage lines and utility services.

Hydroseeding2.11.2


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DefinitionThe application of a protective layer of straw orother suitable material to the soil surface.

PurposeTo protect the soil surface from the erosive forcesof raindrop impact and overland flow. Mulchingalso helps to conserve moisture, reduce runoffand erosion, control weeds, prevent soil crustingand promote the establishment of desirable

vegetation.

ApplicationThis practice applies to any site where vegetationestablishment is important for the protectionof bare earth surfaces. Mulching provides amicroenvironment creating suitable conditions forgermination and rapid growth.

Mulching can be used at any time where theinstant protection of the soil surface is desired.Mulching can be used in conjunction with seedingto establish vegetation, or by itself to providetemporary protection of the soil surface.

Mulching is also used during the winter months

Mulching2.11.3

germination will be too slow to establish effectivegrass cover using conventional sowing methods.



Before mulching install any erosion and

sediment control practices such as runoffdiversion channels and sediment retentionstructures.

MulchingWhen mulching using a machine, use unrottedsmall grain straw applied at a minimum rateof 4000 kg per ha. Hand application of mulchwill require a higher rate as the application isnot as even. If straw is difficult to source haycan be used, however the application rate islikely to be higher.

Ensure the material is free of any noxiousplants. Mulching needs to be spread uniformlyand secured to the soil surface. For smallerareas hand spreading of mulch material can

Plate 5: Mulching


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DefinitionThe establishment and permanent stabilisation ofdisturbed areas by laying a continuous cover ofgrass turf.

PurposeTo provide immediate vegetative cover to stabilisesoil on disturbed areas such as. For example: Critical erosion prone areas on the site. Critical areas on the site that cannot be

stabilised by conventional sowing methods. Runoff diversion channels and other areas

of concentrated flow where velocities will notexceed the specifications for a grass lining.

ApplicationTurfing is the preferred method for disturbedareas that must be immediately stabilised. It isparticularly useful for:

Watercourses and channels carryingintermittent flow.

Areas around drop inlets. Residential or commercial lawns to allow

prompt use and for aesthetic reasons. Steep areas.

Turfing2.11.4

DesignWhile there are no specific design criteriafor turfing, turf reinforced with geosyntheticmatting should be considered for areas of higherosion potential; for example, steep slopes orconcentrated overland flow paths.


Before turfing, properly prepare the site

to ensure the successful establishment ofvegetation. This includes applying fertiliser as inTable 7 of these guidelines, uniformly gradingthe area, clearing all debris, removing stonesand clods and scarifying hard packed surfaces.

Turf InstallationDuring periods of high temperatures, lightlyirrigate soil immediately before laying turf.

Lay the first row of turf in a straight line, withsubsequent rows placed parallel to and tightlywedged against each other. Stagger lateraljoints in a brick-like pattern. Do not stretch oroverlap turf and make sure all joints are buttedtight to prevent voids, which can cause dryingof the grass roots.

Plate 7: Turfing


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On sloping areas or channels where erosionmay be a problem, lay turf downslope with theends of the turf material overlapped such thatthe upslope turf overlaps the downslope turf byat least 100 mm. It may be necessary to securethe turf with pegs or staples. Ensure the turf atthe top of the slope is appropriately trenched into prevent runoff moving underneath it.

As turfing is completed in one area, roll ortamp the entire area to ensure solid contactof the grass roots with the soil surface. Afterrolling, immediately water the turf until theunderside of the new turf and soil surfacebelow the turf are thoroughly wet.

Maintenance- Water daily during the first week of laying

unless there is adequate rainfall.- Do not mow the area until the turf is firmly

rooted.- Apply fertiliser regularly as in Table 7 of

these guidelines uniformly.


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DefinitionThe artificial protection of channels and erodibleslopes utilising artificial erosion control materialsuch as geosynthetic matting, geotextiles orerosion matting.

PurposeTo immediately reduce the erosion potential ofdisturbed areas and/or to reduce or eliminateerosion on critical sites during the periodnecessary to establish protective vegetation. Someforms of artificial protection may also help toestablish protective vegetation.

Application On short steep slopes. On areas that have highly erodible soils. In situations where conventional mulches are of

limited effectiveness in withstanding high runoffvelocities.

In channels (both perennial and ephemeral)where the design flow is greater than in-situsoil can withstand.

In areas where there is not enough room toinstall adequate sediment controls.

In critical erosion-prone areas such as sedimentretention pond outlet and inlet points.

In areas that may be slow to establish anadequate permanent vegetative cover.

In areas where the downstream environment isof high value and rapid stabilisation is needed.

DesignThere are two categories of GECS: temporary

degradable and permanent non-degradable.

Temporary Degradable GECSThese are used to prevent loss of seedbedand to promote vegetation establishmentwhere vegetation alone will be sufficient forsite protection once established. Commontemporary GECS are erosion control blankets,open weave meshes/matting and organicerosion control netting (fibre mats factorybonded to synthetic netting).

Permanent Non-Degradable GECS

These are used to extend the erosion controllimits of vegetation, soil, rock or othermaterials. Common permanent GECS arethree-dimensional erosion control and re-

ll l f

Geosynthetic Erosion Control Systems (GECS)2.12

The selection of an appropriate GECS is acomplex balancing of the relative importance ofthe following requirements. Endurance: durability, degree of resistance to

deformation over time and ultraviolet radiationand to chemicals (natural or as pollutants).

Physical: thickness, weight, specific gravity anddegree of light penetration. Generally a thicker,heavier material will provide better protection.

Hydraulic: ability of the system to resist tractiveshear strength and protect against channelerosion, erosion of underlying soils or slopeerosion from rainfall impact.

Mechanical: deformation and strengthbehaviour. Tensile strength and elongation,stiffness (how well it will conform to thesubgrade) and how well it will resist tractiveshear forces.

When a geotextile is to be used for temporarychannel or spillway protection, considercombining a high strength, low permeability clothover a soft pliable needle punch cloth pinned toensure the cloth is in contact with the entire soilsurface. Trench and pin all flow entry points such

that the upslope geotextile edge overlaps thedownslope geotextile mat. Toe in the upslope endof the downslope mat.

In high risk areas such as spillways anddiversions, pin geotextiles down on a 0.5 mgrid or in accordance with the manufacturersspecifications, whichever provides the greatestnumber of contact points.

There is a large number of products availablefor all situations and depending on the degree

of protection needed, a product or combinationof products will be available to suit the situation.It is vital that the product used is designed forthe intended use and installed and maintainedaccording to its specifications. Consideration inusing the various GECS available should be usedbased on the following characteristics: sediment yield (generally ranked highest) stability under flow vegetation enhancement durability cost.


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When installing GECS within a channel, it is

important that the design velocity of the product isconsidered and again that the product chosen isappropriate for the use.

Many products provide for the combination of are-vegetation technique and an artificial erosion

control measure. Again, design specifications

need to be closely followed in all cases.

MaintenanceInspect after every rainfall and undertake anymaintenance immediately.

Figure 11: Geotextile Laid on Slope


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DefinitionA stabilised pad of aggregate on a filter clothbase located at any point where traffic will beentering or leaving a construction site.

PurposeTo prevent site access points from becomingsediment sources and to help minimise dustgeneration and disturbance of areas adjacent tothe road frontage by giving a defined entry/exitpoint.

ApplicationUse a stabilised construction entrance at allpoints of construction site ingress and egress,with a construction plan limiting traffic to theseentrances only. They are particularly useful onsmall construction sites but can be utilised for allprojects.

Design

Clear the entrance and exit area of allvegetation, roots and other unsuitable materialand properly grade it.

Provide drainage to carry runoff from thestabilised construction entrance to a sediment

Stabilised Construction Entrance2.13

Place aggregate to the specifications below andsmooth it.

Table 8: Stabilised Construction EntranceAggregate Specifications

AggregateSize

50-75 mm washedaggregate

Thickness 150 mm minimum

Length 10 m minimum

Width 4 m minimum

MaintenanceMaintain the stabilised construction entrance ina condition to prevent sediment from leaving theconstruction site. After each rainfall inspect anystructure used to trap sediment from the stabilisedconstruction entrance and clean out as necessary.

When wheel washing is also required, ensure thisis done on an area stabilised with aggregate which

drains to an approved sediment retention facility.

Plate 8: Stabilised Construction Entrance


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Figure 13: Stabilised construction entrance


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DefinitionA temporary pipe structure or constructed flumeplaced from the top of a slope to the bottom.

PurposeDrop structure is installed to convey surface runoffdown the face of unstabilised slopes in order tominimise erosion on the slope face.

ApplicationDrop structures are used in conjunction with runoffdiversion channels/bunds. The runoff diversiondirects surface runoff to the drop structure whichconveys concentrated flow down the face of aslope. If other forms drop structure are beingconsidered, approval of those structures may benecessary on a case by case basis.

Design Construct pipe drop structures and flumes from

watertight materials.

Extend the drop structure beyond the toe of theslope and adequately protect the outlet fromerosion using riprap over a geotextile apron.

Pipe/Flume Drop Structure2.14

Use of the following design criteria for pipedrop structures, is shown in Figure 10.

Table 9: Design Criteria for Pipe DropStructure

Pipe Diameter(mm)

Maximum CatchmentArea (ha)

150 0.05

300 0.2

450 0.6

500

Specific design is required for catchmentsexceeding 1 hectare in area.

Ensure that the runoff diversion channel/bundis at least twice the pipe diameter or height offlume as measured from the invert.

Plate 9: Flume drop structure


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Install a flared entrance section of compactedearth. To prevent erosion, place impermeablegeotextile fabric into the inlet extended aminimum of 1.0 m in front of and to the sideof the inlet and up the sides of the flaredentrance. Ensure this geotextile is keyed 150mm into the ground along all edges andpinned at 500 mm centres.

When the catchment area is disturbed, ensurethe drop structure discharges into a sedimentretention pond or a stable conveyance systemthat leads to a pond. When the catchment areais stabilised, ensure the drop structure outletsonto a stabilised area at a non-erosive velocity.The point of discharge may be protected byrock riprap.

Ensure the drop structure has a minimum slopeof 3 percent.

Construction Specifications for Pipe DropStructures A common cause of failure of pipe drop

structures is water saturating the soil andseeping along the pipe where it connects to therunoff diversion channel/bund. Backfill properlyaround and under the pipe with stable materialin order to achieve firm contact between thepipe and the soil at all points to eliminate thistype of failure. Pipe material used for the dropstructure can consist of rigid pipe materialor flexible pipe as required. If flexible pipematerial is utilised, it is vital that the material befixed to the slope at regular intervals to preventmovement. Rigid pipe can generally be secured

at greater intervals.

Place pipe drop structures on undisturbed soilor well-compacted fill at locations as detailedwithin the Erosion and Sediment Control Planfor the site.

Immediately stabilise all disturbed areasfollowing construction.

Secure the Pipe drop structure to the slope atleast every 4 m. Use no less than two anchors

equally spaced along the length of the pipe.

Ensure all pipe connections are watertight.

Construction Specifications for flumes A common failure of flumes is outflanking

of the flume entrance or scouring of theinvert to the flume. This can be preventedby waterproofing the entrance to the flumeby trenching in an appropriate imperviousgeotextile or plastic liner so that all flows arechannelled directly into the flume. Alternativelya piped entrance can be installed.

Flumes can be constructed from materials suchas corrugated steel, construction ply, sawntimber or halved plastic piping.

Construct the flume to ensure there are noleaks. For wooden or plywood flumes, orflumes where leakage is likely, extend animpervious liner down the full length of theflume structure.

For slopes greater than 30 percent, a flumecan be constructed from a standard 1.2 m x2.4 m x 22 mm plywood sheet (refer to Figure14). This will be adequate for catchments upto one hectare. Specific design is required forlarger catchments.

Fasten the flume to the slope using waratahs orwooden stakes placed in pairs down the slopeat 1 - 4 m spacings depending on the flumematerial used. Fasten the flume to the waratahsor stakes using wire or steel strappings.

Place flumes on undisturbed soil or wellcompacted fill at locations detailed in the sitesErosion and Sediment Control Plan.

Maintenance Inspect the pipe/flume drop structure

periodically and after each rain event.Immediately carry out any maintenancerequired.

Keep the inlet open at all times.


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Figure 14: Pipe/flume drop structures

Figure 15: Flume design specifications (for catchments up to 0.5 ha)


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DefinitionA non-erosive outlet for concentrated runoffconstructed to disperse flows uniformly across aslope.

PurposeTo convert concentrated flow to sheet flow andrelease it uniformly over a stabilised area toprevent erosion.

The level spreader provides a relatively low costoption, which can release concentrated flowwhere site conditions are suitable. Particular careis needed to ensure the level spreader outlet lip iscompletely level and is in stable, undisturbed soilor is well armoured. Any depressions in the levelspreader lip will re-concentrate flows, resulting infurther erosion.

Application Where sediment-free storm runoff can be

released in a sheet flow over a stabilised slopewithout causing erosion.

Where sediment-laden overland flow can bereleased in sheet flow across the inlet to asediment retention pond.

Where the area below the level spreader lipis uniform with the slope of 10 percent orless and/or is stable for the anticipated flowconditions.

Where the runoff water will not re-concentrateafter release.

Where there will be no traffic over the levelspreader.

Level Spreader2.15

Design Determine the capacity of the level spreader byestimating peak flow from the 20-year storm.

Where possible, choose a site for the levelspreader that has a natural contour that willallow for the rapid spreading of flows, forexample, at the end of a knoll or ridge.

Select the appropriate length, width and depthof the spreader from Table 10 below.

Construct a 6 m long transition section in therunoff diversion channel leading up to the levelspreader so the width of the runoff diversionchannel will smoothly meet the width of thelevel spreader to ensure uniform outflow. Thelevel spreader trench tapers down to 1 m at theend of the level spreader.

Maintain a minimum inlet width of 3 m.

Ensure that the grade of the level spreader is0 percent.

Construct the level spreader lip on undisturbedsoil, incorporating a 50 x 15

Documents

Erosion principles